Update vendored development ember.js to 1.0.0-rc.1

Ember was updated to rc1 in https://github.com/emberjs/ember-rails/commit/342ad95e3ddb5dd43ae37200637704175cfb46a0, but the development version of ember.js still shows it as pre4 (see [here](https://github.com/emberjs/ember-rails/blob/342ad95e3ddb5dd43ae37200637704175cfb46a0/vendor/ember/development/ember.js#L1)). This updates `vendor/development/ember.js` to 1.0.0-rc.1.